Hydraulic pumps or motors



o. H. THOMA 3,386,389

HYDRAULIC PUMPS 0R MOTORS 2 Sheets-Sheet 1 `une 4, 1968 Filed May 27, 1966 v r /fV/ /2/ Vg m mm @NQ @L Mmmfu b mw mm, @m QW a INVENToR @sn/4.40 THe/14.4

A'r-memsx June 4, 1968 0. H. THoMA HYDRAULIC PUMPS OR MOTORS 2 Sheets-Sheet z Filed May 27, 1966 INVENTOR 05W/uo h( Zwan/1,4 BY

United States Patent 3,386,389 HYDRAULIQPUMPS OR MOTORS Oswald H. Thoma, Cheltenham, England, assignor to Hydraulic-Drive A.G., Glarus, Switzerland, a cornpany of Switzerland Filed May 27, 1966, Ser. No. 553,516 6 Claims. (Cl. 10S-162) ABSTRACT 0F THE DISCLOSURE A rotary hydraulic motor having a number of doubleended rotating axial cylinders each containing pairs of separate opposed pistons cooperating with inclined cam plates at opposite ends of the machine, and valve means with axially facing surfaces for admitting and discharging hydraulic fluid from the cylinders, the twlo pistons of each pair being of different diameters and sliding in cylinder bore sections of different sizes so that the resultant differential pressure urges the cylinder block towards the stationary valve member.

This invention relates to axial piston hydraulic pumps or motors vof the opposed piston type, which will be referred to for convenience herein as opposed piston machines. Such machines comprise in general a rotary member formed with a number of parallel cylinder bores spaced around its axis, each cylinder containing a pair of opposed pistons which react respectively against inclined cam surfaces or swash plates at opposite ends of the machine. Thus as the rotary member rotates, when the machine is used as a pump, the pistons reciprocate in opposition causing displacement of the fluid within the cylinders, or when used as a motor, supply of fluid under pressure to selected cylinders causes rotation of the machine.

The invention relates particularly to an opposed piston machine in which the admission and discharge of uid to and from the cylinders is controlled by a rotary valve member cooperating with a non-rotary distributing plate, the Huid member and the plate having co-acting sealing surfaces which lie generally transverse t-o the rotary axis. This type of distributor plate may be referred to generally as an axial timing plate as opposed to a radial or pintle type of valve where the opposed surfaces of the valve member and the distributor member are generally cylindrical.

It is an object of the invention t-o provide an improved opposed piston machine which will be capable of operating as a high speed, high torque, motor, or as a high speed, high capacity, pump. For such applications it is essential that the machine should be capable of handling comparatively large volumetric rates of flow and this entails fluid admission and discharge passages of large cross-sectional area. If the cross-sectional area of the ports in the valve member and the timing plate are increased inevitably there is an increase in the resultant pressure forces acting on the valve member and the distributor plate in a direction tending to separate these two parts. Since the distributor plate is non-rotary the pressure reaction can be resisted without difficulty from a stationary part of the casing of the machine. In the case of the rotary valve member, however, this increased pressure reaction load is imparted as an axial thrust on the main rotary member of the machine and would tend to exert an undesirable end load on the thrust bearings of the machine. An object of the invention accordingly is to provide means for reducing or eliminating this undesirable end load, but the invention is also of utility in conventional machines of normal llow capacity, since it reduces the loads on the thrust bearings of the machine.

Now in accordance with the invention an axial piston pump or motor comprises a rotary member provided with spaced cylinders parallel to the axis of rotation, each containing a pair of opposed pistons, a non-r0tary cam member at each end of the rotary member, each cam member having a surface inclined, or capable of being inclined, to a plane perpendicular to the axis of rotation, and means acting between the pistons and the cam surfaces to cause rotation of the rotary member as the pistons reciprocate, or vice versa, uid admission and discharge passages connected to a non-rotating distributing member, a rotating valve member connected to rotate with the rotary member and abutting axially against the non-rotating distributing member, the valve member having ports in its axial end surface which engages the distributing member, each port commnuicating with one of the said cylinders, and in which the two pistons of each pair are of different effective areas, and the opposite ends of each cylinder are of correspondingly different internal cross-section, whereby a resultant differential pressure acts on the rotary member in a direction towards the distributing member.

Thus it will be seen that the difference in effective areas between each pair of opposed pistons results in a differential pressure force being exerted on the respective cylinder, this differential force being imparted through the piston of larger effective area from the respective inclined cam surface. The resultant axial force is transmitted from the rotary member to the rotary valve member and is therefore not transmitted through the bearings which support the rotary member.

It will be understood that although the cam members are essentially non-rotary they may be capable of angular adjustment about the rotary axis, for the purpose of altering the capacity of the pump. Similarly the nonrotary distributor member may be capable of angular adjustment about the rotary axis `for timing purposes.

According to a preferred feature of the invention the cylinders in the rotary member are formed by separate hollow cylindrical sleeves which have stepped internal bores, and the sleeves may be insertable into locating apertures in the rotary member from one end, and have enlarged external flanges acting as locating abutments at the said end.

In a preferred embodiment the rotary member comprises a main hollow tubular assembly, supported by bearings at oposite ends from a casing, and the rotary valve member forms an internal transverse wall within the hollow tubular assembly, the distributor plate being mounted adjacent the rotary valve member within one end of the hollow tubular assembly. In this construction the distributor plate is preferably connected to a stationary part of the casing of the machine by two axially extending' parallel tubes, which are flexibly connected at opposite ends respectively to the distributor plate and to the casing, the tubes also constituting fluid admission and discharge conduits. Moreover the distributor plate may be connected to a stationary part of the casing by two further parallel tubes rigidly connected together and constituting a torsion element preventing the distributor plate from pivoting about the axis of the machine.

The invention may be performed in various ways and one speciiic embodiment will now be described by way of example with reference to the accompanying drawings, in which FIGURE l is a longitudinal section through a hydraulic motor according to the invention, and

FIGURE 2 is a cross section through the motor of FIGURE l, the left hand side being in section on the line II-II, and the right hand Side in section on the line III-Ill of FIGURE 1.

In this example the invention is applied to a high torque axial piston hydraulic motor of the opposed piston type, comprising a cylindrical casing 1li closed at one end by an end plate 11, within which casing is mounted a rotary member supporting eleven cylinders equally spaced about the axis. At opposite ends of the casing there are provided annular cam members 12, 13 fixed in the casing each having an annular cam surface 14 inclined at an angle of approximately 15 to a plane perpendicular to the axis.

The rotary member is formed in three main parts, namely two hollow end parts 15, 16, each having a radial flange 17 at its inner end, and an intermediate substantially at circular plate-like part 1S sandwiched between the two flanges, and constituting the rotary valve member. The two end parts 15, 16 are supported in roller thrust bearings 19, 2li from the casing of the machine and the end part at the open end of the casing has internal splines 21 by which is can |be connected to an output shaft of the motor.

The two llanges 17 on the end parts 15, 16 and the intermediate plate-like part 18 are formed with eleven aligned apertures spaced around the axis of rotation to receive eleven cylinder sleeves 22, each sleeve projecting axially a substantial distance beyond the respective llange. Each cylinder sleeve can be formed of a suitable material different from that of the rotary member, and can be suitably heat treated, machined and linished independently of the three component parts 15, 16, 18, of the rotary member. Within each cylinder sleeve are mounted a pair of opposed pistons 25, 26, the pistons being urged apart by a spring 27 and each piston having a spherical socket at its outer end to receive the spherical ball 28 on a sliding slipper 29 engaging the respective annular cam surface 14. The two pistons of each pair are of different etective areas, the piston at the open end of the machine being of larger diameter.

From the mid-point of each cylinder sleeve 22 a radial iiuid passage 30 extends inwards through the sleeve and the rotary valve member, to intersect an axially extending passage 31 which opens into a port 32 at the planar axial end face 33 of the valve member remote from the open end of the machine. These axial and radial passages 30, 31 are of comparatively large diameter to accommodate the relatively high volumetric rates of flow contemplated by the invention, and the increased areas of the ports 32 necessarily pro-duce an increased area at the said face 33 of the valve member on which the hydraulic pressure lluid acts in a direction towards the open end of the machine.

To accommodate the pistons 25, 26 of different crosssectional areas each cylinder sleeve 22 has an internal bore which is correspondingly of relatively large diameter at the open end of the machine and of relatively small diameter at the opposite end. For example the bore may have an internal diameter of 31 mm. at one end an internal diameter of 25 mm. at the other end. The step or internal shoulder 34 is positioned approximately at the mid-point in the length of the sleeve and this provides in effect an annular pressure surface on which the fluid pressure exerts a force acting in an axial direction away from the open end of the machine. The major part of the length of the cylinder sleeve is of uniform external diameter but the portion 35 of the sleeve which projects beyond the locating apertures in the components of the rotary member, at the open end of the machine, is of slightly enlarged external diameter this providing an annular abutment. The differential pressure forces acting on the cylinder sleeve thus tend to force the sleeve towards the closed end of the machine and so urge this abutment 35 on the sleeve against the adjacent face on the rotary member, this thrust being transmitted through the rotary member to the rotary valve member 18. The effective differential pressure force exerted by those cylinders which are under pressure at any instant is designed to counterbalance almost exactly the force in the opposite direction generated by the pressure fluid at the sealing face 33 of the rotary valve member. The dilerential pressure force also acts as a locating force which at all times holds the cylinder sleeves in position in the rotary member. It is therefore unnecessary to provide any locking means or detent to hold each cylinder sleeve in position, and withdrawal of the sleeves when necessary for repair or replacement is facilitated.

This construction also provides an increased thickness in the wall of the cylinder sleeve 22 at both ends which project from the locating apertures in the rotary member. This is of considerable advantage in that these projecting parts of the sleeve are required to absorb the lateral -forces generated by the sliding slippers 29 and are therefore subject to considerable bending moments.

Each sleeve has a radial aperture 36 at its midpoint designed to communicate with one of the radial passages 30 in the rotary Valve member and to prevent the cylinder sleeve rotating in its aperture a locking ring 37 is fitted on one of the tubular parts of the rotary member, this ring engaging in a cut-away at the adjacent end of the sleeve to prevent the sleeve rotating.

The end plate 11 -at the closed end of the machine is .formed with two diametrically opposed through-passages 4t), 41, constituting inlet and outlet passages. On the internal side of this end plate the passages issue into cylindrical sockets or recesses in which are mounted the ends of two elongated fluid pipes 42, 43. These pipes extend within the respective hollow end part 16 of the rotary member and at their opposite ends the pipes seat in two corresponding sockets in a non-rotary timing plate 44. Two further diametrically opposite pipes (one of which is shown at 45 in FIGURE 2), similarly connected to the end plate 11 of the casing and to the timing plate 44, are rigidly interconnected by a Welded web 46 to increase the torsional stillness of the pipes which therefore hold the timing plate against rotation. The timing plate 44 has a substantially at end surface 47 arranged to bear directly on the corresponding flat surface 33 of the intermediate part 18 of the rotary member, which constitutes the rotary valve member. A stub or spigot 48 mounted centrally in the timing plate 44 seats in a central recess in the rotary valve member to hold the two in alignment on the rotary axis. The two fluid pipes 42, 43, each communicate with one of two opposed kidney-shaped fluid ports 49 in the distributor or timing plate, and the two pipes 4S are also connected respectively each to one of the ports 49.

The effective area over which the uid pressure acts on the non-rotary distributor plate 44 in a direction away from the rotary valve member 18 is considerably greater than the opposing area on the opposite side of the distributor plate over which the liuid pressure acts, namely the combined area of one of the pipes 42, 43, and one pipe 45. The resultant force tends to urge the distributor plate 44 away from the rotary valve member 18 towards the closed end of the machine. This axial force is transmitted through the four elongated pipes 42, 43, 45 which seat at their opposite ends in recesses in the end plate 11 of the machine so that the end thrust is counteracted by the casing itself. Each of these fluid pipes 42, 43, 45 is itself hydraulically balanced.

In the embodiment described the differential pressure force is designed to counterbalance almost exactly the force in the opposite direction generated by the pressure iluid at the sealing face 33 of the rotary valve member. In certain applications, however, it may be preferred to adopt an effective differential pressure area of a lower size, in order to obtain the largest possible volumetric capacity, and in this case the effective differential presure force will only partly counterbalance the forces acting on the rotary valve member in the opposite direction, the out of balance axial thrust being absorbed by the thrust bearings of the machine.

I claim:

1. An axial piston pump or motor comprising a rotary member provided with spaced cylinders substantially parallel to the axis of rotation, each containing a pair of separately movable opposed pistons, a non-rotary cam member located at each end of the rotary member, each cam member having a surface inclined, or capable of being inclined, to a plane perpendicular to the axis of rotation, and means acting between the respective pistons of each pair and the said cam surfaces to cause rotation of the rotary member as the pistons reciprocate, or vice versa, a non-rotating distributing member having an axially directed face in which are formed lluid vadmission and discharge passages, a rotating valve member connected to rotate with the rotary member and having an axially directed surface abutting axially against the said face of the non-rotating distributing member, the valve member having ports in the axial end surface thereof which engages the distributing member, each port c0mmunicating with one of the said cylinders, and in which the two pistons of each pair are of ditcrent effective areas, and the opposite ends of each cylinder are of correspondingly dilerent internal cross section, whereby a resultant differential pressure acts on the rotary mem- -ber in a direction towards the distributing member.

2. An axial piston pump or motor according to claim 1, in which each cylinder in the rotary member is formed by a separate hollow cylindrical sleeve which has a stepped internal bore providing a bore section of larger internal diameter at one end to receive the piston of larger diameter, and a bore section of smaller internal diameter at the other end to receive the piston of smaller diameter.

3. An axial piston pump or motor according to claim 2, in which the sleeves are insertable into locating apertures in the rotary member from one end, and have enlarged external flanges acting as locating labutments at the said end.

4. An axial piston pump or motor according to claim 1, in which the rotary member comprises a main hollow tubular assembly, supported by bearings at opposite ends from a casing, and the rotary valve member forms/an internal transverse wall within the hollow tubular assembly, the distributor member being mounted adjacent the rotary valve member within one end of the hollow tubular assembly.

5. An axial piston pump or motor according to claim 1, in which the effective differential pressure force substantially fully counterbalance the opposing pressure force exerted on the ported axial end face of the rotary valve member.

6. An axial piston pump or motor according to claim 1, in which the effective differential pressure force only partly counterbalances the opposing pressure force exerted on the ported axial end face of the rotary valve member.

References Cited UNITED STATES PATENTS 2,273,468 2/1942 Ferris 103-161 2,431,686 12/1947 Deschamps 103-173 2,577,242 12/1951 Grad 103--162 2,525,498 10/1950 Naylor et al. 103-161 2,601,830 7/1952 Berlyn et al 103-162 X 2,646,754 7/1953 Oupr Bede 103-161 3,169,488 2/1965 Galliger 919-199 3,166,016 1/1965 Thoma 103--162 3,200,762 8/ 1965 Thoma 103-162 FOREIGN PATENTS 1,343,916 1l/1963 France. 622,787 7/ 1961 Italy.

DONLEY I. STOCKING, Primary Examiner.

WILLIAM L. FREEH, Examiner. 

